This invention relates to a color television camera and, more particularly, to a color television camera in which the shading correction and white balance correction can be automatically done.
A color television camera receives light from an object and produces a luminance signal and a chrominance signal corresponding to the incident light information, and various types of color television cameras have been proposed.
FIG. 1 is a block diagram showing a conventional single tube color television camera. Referring to FIG. 1, an image pick-up tube 1 has a color separation stripe filter of cyan and yellow. Illustrated in FIG. 1 are a pre-amplifier 2 for amplifying a video signal produced from the image pick-up tube 1, a low-pass filter 3 for trapping the carrier of the amplified video signal output of the pre-amplifier 2, a process amplifier 4 for amplifying a Y (luminance) signal output of the low-pass filter 3, a variable resistor 5 adapted to control the gain of the process amplifier 4, a band-pass filter 6 for passing the carriers of R (red) and B (blue) signals, an R/B separator for separating the R and B signals from the band-pass filter output, a detector 8 for detecting the R signal, a detector 9 for detecting the B signal, a process amplifier 10 for amplifying the R signal output of the detector 8, a variable resistor 11 adapted to control the gain of the process amplifier 10, a process amplifier 12 for amplifying the B signal output of the detector 9, a variable resistor 13 adapted to control the gain of the process amplifier 12, a matrix output circuit 14 receiving the Y, R and B signals to produce Y, (R - Y) and (B - Y) signals, an encoder 15 for producing an NTSC video signal from the output signals of the matrix output circuit 14, and an NTSC output terminal 16. A shading correction circuit 17 feeds shading correction signals to the R and B signal process amplifiers 10 and 12. It includes input terminals 18 and 19 for receiving external horizontal drive (HD) and vertical drive (VD) signals. It also includes a horizontal parabolic wave generator 20 for producing a parabolic wave signal controlled by the HD signal, a horizontal saw-tooth wave generator 21 for producing a horizontal saw-tooth wave signal controlled by the HD signal, a vertical parabolic wave generator 22 for producing a parabolic wave signal controlled by the VD signal, and a vertical saw-tooth wave generator 23 for producing a vertical saw-tooth wave signal controlled by the VD signal. It further includes variable resistors 24 to 35. The variable resistor 24 is adapted to control the horizontal parabolic wave signal which is fed to the B signal process amplifier 12. The variable resistor 25 is adapted to control the horizontal parabolic wave signal which is fed to the R signal process amplifier 10, the variable resistor 26 to control the horizontal saw-tooth wave signal which is fed to the B signal process amplifier 12, the variable resistor 27 to control the horizontal saw-tooth wave signal which is fed to the R signal process amplifier 10, the variable resistor 28 to control the vertical parabolic wave signal which is fed to the B signal process amplifier 12, the vertical resistor 29 to control the vertical parabolic wave signal which is fed to the R signal process amplifier 10, the variable resistor 30 to control the vertical saw-tooth wave signal which is fed to the B signal process amplifier 12, the vertical resistor 31 to control the vertical saw-tooth wave signal which is fed to the R signal process amplifier 10, the variable resistor 32 to control a horizontal parabolic wave signal for dynamic focusing correction, the variable resistor 33 to control a horizontal saw-tooth wave signal output for dynamic focusing correction, the variable resistor 34 to control a vertical parabolic wave signal output for dynamic focusing correction, and the variable resistor 35 to control a vertical saw-tooth wave signal output for dynamic focusing correction. The shading correction circuit 17 further includes fixed resistors r for setting the current levels of the individual signals. A dynamic focusing amplifier 36 amplifies the individual wave signal outputs for dynamic focusing correction to a fixed level to be coupled through a capacitor 37 to a focusing electrode in the image pick-up tube 1. The image pick-up tube 1 is supplied with a high voltage from a high voltage circuit 38 for its operation.
With the color television camera having the above construction, the video signal obtained from its NTSC signal output terminal 16 contains an amplitude distortion, in other words, "shading" which is introduced for various reasons. Accordingly, shading correction is usually done using the shading correction circuit 17. Usually, this shading correction for horizontal and vertical video signals is done in a total of 12 circuit connections for modulation shading and dynamic focusing of the red (R) and blue (B) channels, using the variable resistors 24 to 35 respectively connected to the parabolic wave generators 20 and 22 and saw-tooth wave generators 21 and 23. The adjustment of all the variable resistors 24 to 35, however, is time-consuming In addition, the adjustment level will differ with the individual operators, giving rise to irregularity of the picture quality.